Electromagnetic relay of the bistable type



Sept- 6, 1966 G. KOEHLER ELECTROMAGNETIC RELAY OF THE BISTABLE TYPE Filed Nov. 9, 1964 4.- Sheecs-Sheet 1 Ava/rm? GERARD kofA/L EA Sept. 6, 1966 G. KOEHLER ELECTROMAGNETIC RELAY OF THE BISTABLE TYPE 4 Sheets-Sheet 2 Filed Nov. 9, 1964 GEE/14w Kat-H45 Sept. 6, 1966 G. KOEHLER ELECTROMAGNETIC RELAY OF THE BISTABLE TYPE Filed Nov. 9, 1964 4 Sheets-Sheet 3 bvyavme v o owoi o Hrry.

United States Patent 8 Claims. (01. 345-78) This invention relates to electromagnetic relays comprising an electromagnet provided with an element with residual magnetism and having the special feature of being of the bistable type.

An electromagnetic relay of conventional type returns to its position of rest as soon as the electromagnet which acts on the movable armature ceases to be fed with current. If this relay is controlled by impulses it follows the rhythm of these impulses. It is said to be monostable when its coil is not energized.

To keep a relay in the working position at the end of a control signal, it is known art to establish a second path of excitation of the relay winding through a holding contact of the same relay. This device however has the disadvantage that the memory of the control signal is lost if the supply voltage is accidentally cut oif.

To avoid this drawback it has been proposed to use two magnetic circuits with a mechanical locking system, consisting of a catch which keeps the first circuit in the working position until operation on the second circuit frees the first. In this case however, the size of the relay is doubled and it comprises mechanical members which can wear out and may permit an unlocking under the action of a shock or mechanical stress.

Bistable relays are also known comprising an E-shaped fixed magnetic circuit having a control winding on its central branch and a movable armature consisting of a permanent magnet which pivots on the said branch. By reversing the direction of current in the winding, the relay is caused to rock.

Another known bistable relay comprises a permanent magnet placed in series with the fixed core of its electromagnet. The magnetic circuit of this relay has two opposed air gaps acting on the armature. In this type the permanent magnet is of the ferritic type with a high coercivity and cannot be demagnetized. This relay passes from one state to the other under the effect of control impulses with opposed signs.

The above two types of relay have various drawbacks: the magnetic circuit takes up a god deal of space and gives the relay a particular form, differing from that of ordinary monostable relays, which restricts its possibilities of application. As the armature of the relay has an unstable central position, these relays call for delicate adjustment of the opposed air gaps. Furthermore, if the movable armature of the relay is accidentally brought into the closed position, it remains in this position because of the attraction of the magnet.

This invention is intended to remedy the above mentioned disadvantages, making it possible to obtain a bistable relay controlled by impulses, with an element with residual magnetism, but having only a single magnetic circuit, without opposed air gaps and comparable as regards arrangement and space taken up with a conventional monostable relay, which ensures wide possibility of application. Furthermore, the stable equilibrium position of this relay, controlled by the last control impulse, is not changed even if it is attempted to move the armature to the other position by an exterior mechanical means.

According to the invention, there is provided a bistable Patented Sept. 6, 1966 electromagnetic relay comprising an electromagnet whose magnetic circuit has an element with residual magnetism and whose movable armature is pulled in the rest position by a resilient return member, characterized in that the element with residual magnetism consists of a core ar ranged along the axis of the electromagnet and capable of being magnetized and then partly demagnetized by electric control impulses with opposed signs fed into the winding of the electromagnet, in that the movable armature consists of a core sliding along the said axis, and in that in the working position for which the core with residual magnetism is magnetized, the force of magnetic attraction is greater than that of the resilient return member, while in the rest position for which the said core is partly demagnetized, the return force of the resilient members pretponderates, even with minimum air gap, over the attraction due to the residual magnetism.

Preferably the element with residual magnetism constitutes the fixed core of the electromagnet.

The relay being thus arranged, the two equilibrium positions of the movable core are stable. Even if following a shock or any other cause the movable core is brought from the rest position to the Working position and even if it is kept there by an exterior force for a considerable period, as soon as the disturbing cause is removed, the core returns to its rest position. On the other hand in the working position, the force of attraction of the residual magnetic element is such that it is impossible to displace the movable core, even as a result of a shock which is several tens of times the acceleration due to gravity.

Furthermore, the fact that the movable core acts like a plunger core in relation to the electromagnet makes possible, due in particular to the air gap being located at the point where the flux is a maximum, a wide variation in the magnetic resistance when the relay passes from the working position to the rest position and vice versa. This feature, combined with the range in intensity of magnetization of the fixed core under the effect of the control impulses, makes it possible to obtain towards each of the stable equilibrium positions a considerable return force. Preferably, the fixed core with residual magnetism is formed from a magnetic material of low coercivity, such as an alloy of the ni-ckel-aluminium-cobalt type.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a partly broken view in elevation showing a relay embodying the invention in the rest position.

FIG. 2 is an exploded view in perspective of the various elements forming the relay.

FIG. 3 is a view in :axial section on a larger scale of the relay in the rest position.

4 is a similar view of the relay in the working position.

FIG. 5 is a view in section taken along the line VV in FIG. 3.

FIG. 6 is a diagram of forces in relation to the air gap relative to the magnetic circuit of the above relay.

FIG. 7 is an explanatory diagram of the mechanical control of the movable contacts, and

FIGS. 8 and 9 are two wiring diagrams relating to two methods of feeding the relay with current.

In FIGS. 1 to 5 can be seen the arrangement of a bistable relay in accordance with the invention, designed to have an appreciable cut-off power (for instance ten amperes at volts AC). The relay consists essentially of an electromagnet 1 with an axial plunger core 2 supporting movable contacts 3. The electromagnet 1 is carried by an insulating frame 4 on which are fixed groups of working contacts 5 and rest contacts 6.

This assembly will now be described in more detail.

The electromagnet 1 comprises at least one control winding 11 (FIGS. 3 and 4) accommodated in an electrically insulating housing 12 which has an axial duct 13. One of the flanges 14 of the housing 12 is supported on the base 15 of the yoke 16 of the electromagnet 1 which has at its other end two bent-over lugs 17. On the lugs 17 is fixed by screws a soft iron collar 18 carrying an axial sleeve 19 in which is mounted the fixed core 21 of the electromagnet 1. The core 21 is cylindrical with a circular section.

In accordance with the invention, the core 21 which is engaged in the duct 13 of the housing 12 is made from a material of low coercivity capable of being magnetized or demagnetized by a restricted number of ampere-turns produced by the winding 11. For instance, a nickel aluminium-cobalt alloy may be used with an orientated magnetic temper. Such an alloy is known for instance under the name of Ticonal 600.

The fixing of the core 21 may be eflected in particular by means of an adhesive 22 of polymerizable plastic material, this fixing making it possible to adjust the core to the exact position desired.

The movable core 2, for instance the soft iron has a cylindrical body 23 co-axial with the core 21 and mounted to slide easily in the duct 13. Beyond the base 15 of the yoke 16 the core 23 has a collar 24 also of soft iron and similar to the fixed collar 18. The travel of the movable core 2 is such that in the rest position (FIG. 3) a maximum air gap E is preserved between the facing surfaces 25, 26 of the cores 21 and 23, while in the working position, the air gap issubstantially reduced and becomes equal to e (FIG. 4) corresponding to its minimum value. This air gap e may furthermore be zero, this arrangement not in any way preventing the correct working'of the relay as will be seen. However, to avoid any deterioration due to concussion of the core 21, which may be made of an alloy of low mechanical strength, a residual air gap e of a value which is very low but not zero is preferably preserved between the surfaces 25, 26 in the working position.

The movable contacts 3 are carried by an articulation system with an amplification of movement termed a W type system, known per se and having two pairs of insulated arms of cast material 31 carrying pivots 32 enabling them to pivot in bearings 33 formed by curved lugs of a plate 34 fixed on the collar 24 by a rivet 35. The arms 31 each carry a flexible strip 36 fixed by a projection 37 and supported on a shoulder 38 provided at the free end of the arm 31. The strip 36 is terminated by one of the movable contacts 3. Considering the arrangement provided the relay thus comprises four movable contacts.

Each arm 31 also carries a bracket 39 surrounding the strip 36 and provided with a retaining socket 41 for a flexible strip 42 constituting one of the resilient return members provided for the core 2 and tending to bring it into the rest position. Each strip 42 is fixed to the yoke 16 by screws 43. Without bending, the strips 42 would be parallel to the yoke 16. are maintained with a certain amount of camber by the sockets 41, as shown in FIG. 3, and thus tend to spread the arms 31 apart. 1

The insulating frame 4, of cast material for instance, carrying the fixed contacts 5 and 6 (numbering eightin all) comprises four square section uprights 45 attached to a fixed base 46 traversed by connecting tongues 47 and 48' carrying the fixed contacts 5 and 6 respectively. Other tongues 64 (FIG. 2) act as connections for the winding 11 via flexible conductors 63 and as connections for the movable contacts 3 via flexible conductor 65 (FIGS. 1 and 2).

The forces applied to the movable core 2 are represented in the graph in FIG. 6 where the value of the air gap separating the surfaces and 26 is plotted along OX In the rest position they and the values of the forces corresponding to the different conditions of excitation, independently of their direction, are plotted along OY. At J and K are represented the points respectively corresponding to the rest (air gap E) and working (air gap e) positions. The characteristic curve of the resilient return members constituted by the strips 42 is given by the curve HG. The characteristic curve of the force of magnetic attraction exerted on the core 2 .by the winding 11 (assumed to be excited) is given by the curve BC situated above the preceding one, it being understood however that this force is in the opposite direction to the preceding.

It is arranged according to one of the features of the present invention that the force of attraction exerted on the core 2 by the single fixed core 21, when the winding 11 is not energized, corresponds at rest to a point A situated below the point G. Further, this force corresponds in the working position to a point D situated above the point H.

Under these circumstances when the movable core 2 is in the rest position the residual force JA due to the magnet is less than the return force I G. If 'by exterior mechanical action the core 2- is brought to the. position corresponding to the working position (air gap e) the, point A would become A and if it were so arranged that this point were below the point H (which does not present any difliculty as the core 21 can be demagnetized consequently) the action of the spring 42 would remain preponderant so that the core 2 would regain the rest position as soon as the disturbing cause ceased.

When the ampere-turns corresponding to the pull impulse are fed into the winding 11, a force of attraction J B is available which is greater than the mechanical return force JG. The core 2 moves towards the core 21, the air gap diminishes so that the force of magnetic attraction increases in accordance with a known law (arc BC).

In the working position for which the air gap :2 is a minimum (and possibly zero) the force of attraction is As in the working position the magnetic resistance of the magnetic circuit is low the pull excitation ensures, as soon as the core 2 has reached the working position, an effective magnetization of the core 21.

When the pull impulse then ceases the force due to the core 21 being thus magnetized is KD which is greater than the return force KH of the spring.

During the movement of the core 2 towards the working position, the arms 31 are drawn by the collar 24 and by the bearings 33. Because'of the support of the strips 42 in the sockets 41 this movement is accompanied by a rotation of the arms 31 in the direction f (FIG. 4) round their pivots 32 and a cambering of the strips 42. The brackets 39 push the strips 36 in such a way that the movable contacts come to rest against the working studs 5.

The type of connection provided between the movable core 2 and the contacts 3 is equivalent to the W system represented in FIG. 7, where the rest position is shown in solid line and the working position in chain line. It can be seen that the movement of the collar 24 (coming to 24) brings the contacts 3 to 3', simultaneously producing an amplification of the amplitude of the movement (easily in a ratio of 1 to 3) and a change in direction of the movement of the driven components in respect of the driving component.

Due to the W type of movement amplification device adopted, it is possible to arrange that the core 2 shall be subjected to a considerable return force and that it has only a slight travel. Such conditions are favorable for the satisfactory return of the core 2.

When the return impulse is fed into the winding 11 for the purpose of bringing the relay to the rest condition, the corresponding ampere-turns bring the figurative point of magnetic attraction at D to a point situated below H.

From this moment the force of return of the spring strips 42 becomes preponderant and causes the movement of the movable core 2 and its return to the rest position. Furthermore, the application of the return excitation ampere-turns causes a partial demagnetization of the fixed core 21. The result is that at the end of this return excitation the residual force of magnetic attraction IA is less than that (JD') which would have been obtained by bringing the core 2 mechanically from its working position to its rest position. Consequently, the force JG of the springs 42 can be rendered substantially preponderant.

In reality because of the time constant of the magnetic circuit, the movement of the core 2 generally begins before the force of magnetic attraction has reached it settled working conditions value for the air gap in question. At the moment when the pull excitation is fed in, this phenomenon has no elfect on the final condition corresponding to the air gap c.

On the other hand, at the moment of application of the return excitation, the increase in the magnetic resistance of the magnetic circuit before the ampere-turns have reached their settled working conditions value, makes it possible to avoid causing a magnetization of the fixed core 21 in the reverse direction.

Thus, even in the case of a variation from single to double of the return ampere-turns of the core 2 in the rest position the inversion of the functions of the relays by inversion of the direction of the magnet is guarded against.

Of course the initial magnetization of the core 21 can be effected by surcharging for a short instant the winding 11 of the electromagnet.

By way of numerical example, for a relay having a cutoff power of a., 110 v., A.C., and the following other features:

Consumption A.C.:

Pull w 7 Dropped back w 3 Consumption D.C.:

Pull w 15 Dropped back w 13 Duration of pull impulse (passage to the working condition):

A.C ms 80 DC. rns

Duration of dropback impulse (pasnage to the rest condition):

A.C. ms 40 D.C. ms 15 The following values were found corresponding to the forces at work:

Thus, the magnetic circuit with the plunger core due to its greater efiiciency (connected with the localization of the air gap at the point where the flux is a maximum) makes it possible to produce in the working condition considerable forces of magnetic attraction. These forces are increased by the contact of the collar 24 and the base 15 which favors the circulation of the flux.

In the rest condition this attraction is relatively weak because of the noticeable increase in magnetic resistance. As furthermore, the core 21 is partly demagnetized by the return impulse, the residual force of magnetic attraction at rest is reduced, which is also favorable to the stability of the mobile core 2.

It will also be noted that the weak magnetic resistance in the working condition easily permits the remagnetization of the fixed core 21 provided the working impulse is of suitable duration.

The combination of means provided by the invention thus gives rise to particularly favorable results, while producing a relay of the same size and the same cut-off power.

To ensure the control of the relay, there may be provided for the winding 11 when the current supplied is D.C. from a source 51 (FIG. 8), two windings 11a, 1111: having a common terminal 52 and connected to terminals 53a, 53b of a change-over switch 54. The source 51 is tapped between the terminal 52 and the change-over switch 54. It is thus possible to adapt the coils 11a, 11b to the nature of the work in question, taking into account the fact that the rest impulse requires fewer ampereturns than that of the working impulse.

In the case of A.C. current supply from a source 55 (FIG. 9), only one coil need be provided for the winding 11. The source 55 is connected to this winding and to a change-over switch 56 whose movable contact serves two circuits mounted in parallel in respect of the winding 11. The first circuit designed to transmit the working impulse has a simple dry rectifier 57 and the second, for the return impulse, has a dry rectifier 58 associated with a resistor 59.

In practice, the components 57, 58 and 59 are united in a block 61 (FIG. 2) fixed by screws 62 to the collar 18, the connections between the block 61 and the connecting strips carried by the base 46 taking the form of flexible conductors (not shown) similar to the conductors 63. The assembly is covered with a removable insulating cover supported on the frame 4.

Obviously the invention is not restricted to the embodiment described, and the control of the movable contacts may be effected starting from the core 2 by any suitable system for the transmission of motion.

In particular, the cores of the electromagnet could have a non-circular section, but a circular section is however preferable. Furthermore, the element with residual magnetism could also be placed on the movable core instead of forming the fixed core.

Furthermore, the feed of the winding 11 could also be made A.C. for one of the impulses and DC. for the other. In the case of a DC control the consumption could be noticeably reduced by interposing a capacitor which would only allow one current impulse to pass.

What I claim is:

1. A bistable electromagnetic relay comprising an electromagnet having a winding with an axial duct provided therein, means to feed said Winding with control impulses of opposite polarities, a magnetic circuit associated with said electromagnet, said circuit comprising a stationary core at least partially housed in said axial duct, a second core slidably mounted along said axial duct between a working position Where the airgap between said both cores is minimum and a rest position where said airgap is maximum, a movable armature fitted on said slidable core, resilient means engaging said armature and tending to return said slidable core toward said rest position, one of said cores being constituted by a magnetic material of low coercivity adapted to be magnetized by those of said impulses having a definite polarity and to be partially demagnetized by those of said impulses having the opposite polarity, the magnetic properties of said one core being so related to said resilient means that when said circuit is open after said magnetization the magnetic force urging said slidable core toward said working position is greater than the force of said resilient means urging said slidable core toward said rest position both in said working position and in said rest position, and when said circuit is open after said demagnetization the force of said resilient means urging said slidable core toward said rest position is greater than the magnetic force urging said slidable core toward said working position both in said rest position and in said working position.

2. A relay according to claim 1 and wherein said movable core is, in the rest position, at least partially engaged into said electromagnet winding axial duct.

3. A relay according to claim 1 and wherein said magnetic material of low coercivity consists of an alloy of the nickel-aluminum-cobalt type with orientated magnetic temper.

4. A relay according to claim 1 wherein in said working position said sliding core is substantially in contact with said stationary core.

5. A relay according to claim 1 and wherein said electromagnet magnetic circuit comprises a yoke fitted around said electromagnetic winding, said yoke having two oppositely facing end-pieces located around said movable core and close to said winding axial duct, said movable core further bearing a prominent collar made of a magnetically permeable material, said collar being adapted for abutment onto said yoke end-pieces when said sliding core is in said working position.

6. A relay according to claim 1 and wherein said electromagnet magnetic circuit comprises a yoke fitted around said electromagnetic winding, said yoke having two oppositely facing end-pieces located around said stationary core, this latter being integral with a prominent collar made of magnetically permeable material, said collar further being fixed onto said yoke end-pieces.

7. A relay according to claim 1 and comprising an insulating frame bearing stationary contacts, means borne by said armature and bearing movable contacts for amplifying the movement of said movable contacts in relation to the movement of said slidable core, said amplifying means comprising at least one articulated W-shaped component fixed on said movable armature and on said insulating frame.

8. A relay according to claim 1 wherein said one core is said stationary core.

References Cited by the Examiner UNITED STATES PATENTS 2,935,656 5/1960 Baker 317123 3,005,890 10/1961 White et al 200-87 X 3,128,418 4/1964- Zupa 3*17-165 BERNARD A. GILHEANY, Primary Examiner.

J. J. BAKER, Assistant Examiner. 

1. A BISTABLE ELECTROMAGNETIC RELAY COMPRISING AN ELECTROMAGNET HAVING A WINDING WITH AN AXIAL DUCT PROVIDED THEREIN, MEANS TO FEED SAID WINDING WITH CONTROL IMPULSES OF OPPOSITE POLARITIES, A MAGNET CIRCUIT ASSOCIATED WITH SAID ELECTROMAGNET, SAID CIRCUIT COMPRISING A STATIONARY CORE AT LEAST PLURALITY HOUSED IN SAID AXIAL DUCT, A SECOND CORE SLIDABLY MOUNTED ALONG SAID AXIAL DUCT BETWEEN A WORKING POSITION WHERE THE AIRGRAP BETWEEN SAID BOTH CORES IS MINIMUM AND A REST POSITION WHERE SAID AIRGAP IS MAXIMUM, A MOVABLE ARMATURE FITTED TO SAID SLIDABLE CORE, RESILIENT MEANS ENGAGING SAID ARMATURE AND TENDING TO RETURN SAID SLIDABLE CORE TOWARD SAID REST POSITION, ONE OF SAID CORES BEING CONSTITUTED BY A MAGNETIC MATERIAL OF LOW COERCIVITY ADAPTED TO BE MAGNETIZED BY THOSE OF SAID IMPULSES HAVING A DEFINITE POLARITY AND TO BE PARTIALLY DEMAGNETIZED BY THOS EOF SAID IMPULSES HAVING THE OPPOSITE POLARITY, THE MAGNETIC PRPERTIES OF SAID ONE CORE BEING SO RELATED TO SAID RESILIENT MEANS THAT WHEN SAID CIRCUIT IS OPEN AFTER SAID MAGNETIZATION THE MAGNETIC 